Photoacoustic waves are a kind of elastic wave that is generated during a thermoelastic process occurring when a substance is irradiated with light in a wavelength range absorbed by the substance. Photoacoustic waves have therefore attracted attention as a method for imaging absorption properties.
A photoacoustic microscope that employs photoacoustic waves as detection signals for the purpose of imaging uses, as excitation light, pulsed light corresponding to a wavelength range that is absorbed by an object under observation. The photoacoustic microscope focuses the excitation light with an objective lens to scan within a specimen using a focused spot and then detects, with a transducer or the like, a photoacoustic wave generated at each focused spot position (see JP 2011-519281 A (PTL 1)). With such a photoacoustic microscope, during the scanning of the specimen with the focused spot, a photoacoustic wave is generated when an absorbing substance is present at the focused spot position. Hence, by detecting the photoacoustic wave, the absorption properties in the specimen can be imaged.